Expression of inducible nitric oxide synthase and p53 in oral epithelial dysplasia

A Case-control Study Comparing and Correlating iNOS Expression among Various Clinicopathological Variants of Oral Leukoplakia and Oral Squamous Cell Carcinoma: A Immunohistochemistry Study

Background and Objective

The role of inducible nitric oxide synthase (iNOS) has been implicated in various pathological processes including oral carcinoma. Oral premalignancy being its precursor lesion is also expected to show similar pattern. This study attempts to appraise the iNOS expression in various clinicopathological stages and grades of oral leukoplakia (OL) and oral squamous cell carcinoma (OSCC).

Materials and Methods

A case-control study design was adopted for this study with a total sample of 90 subjects, distributed equally into the three study groups, namely controls, OL, and OSCC. Clinical staging and histopathological grading for both the case groups were performed. Representative tissue samples from all groups were obtained and studied for iNOS expression using immunohistochemistry (IHC). Data were presented in mean and percentages accordingly. Inferential analysis was performed using Kruskal-Wallis test, Mann-Whitney test, and Spearman rank correlation test.

Results

Significant (P < 0.001) difference was observed among the groups, where 83.3% of OSCC and 73.3% of OL epithelial cells showed iNOS expression. The normal cells did not show up any expression. The expression was found to rise with the progressing clinical stages of OL (P < 0.05) and OSCC (P < 0.01). Similar pattern was observed with respect to advancing dysplasia in OL (P < 0.01) and cell differentiation in OSCC (P < 0.01). Significant positive correlation was found in clinicopathological categories of OL and OSCC. Considering the risk assessment, iNOS staining was found to be significantly raised in advanced cases of OSCC (P < 0.01) and high-risk cases of OL (P < 0.01).

Conclusion

Increased expression of iNOS can be an early diagnostic marker in OL and as prognostic marker in OSCC.

Exogenous Nitric Oxide Suppresses in Vivo X-ray-Induced Targeted and Non-Targeted Effects in Zebrafish Embryos

The present paper studied the X-ray-induced targeted effect in irradiated zebrafish embryos (Danio rerio), as well as a non-targeted effect in bystander naïve embryos partnered with irradiated embryos, and examined the influence of exogenous nitric oxide (NO) on these targeted and non-targeted effects. The exogenous NO was generated using an NO donor, S-nitroso-N-acetylpenicillamine (SNAP). The targeted and non-targeted effects, as well as the toxicity of the SNAP, were assessed using the number of apoptotic events in the zebrafish embryos at 24 h post fertilization (hpf) revealed through acridine orange (AO) staining. SNAP with concentrations of 20 and 100 µM were first confirmed to have no significant toxicity on zebrafish embryos. The targeted effect was mitigated in zebrafish embryos if they were pretreated with 100 µM SNAP prior to irradiation with an X-ray dose of 75 mGy but was not alleviated in zebrafish embryos if they were pretreated with 20 µM SNAP. On the other hand, the non-targeted effect was eliminated in the bystander naïve zebrafish embryos if they were pretreated with 20 or 100 µM SNAP prior to partnering with zebrafish embryos having been subjected to irradiation with an X-ray dose of 75 mGy. These findings revealed the importance of NO in the protection against damages induced by ionizing radiations or by radiation-induced bystander signals, and could have important impacts on development of advanced cancer treatment strategies.

Estimation of salivary nitric oxide in oral precancer patients

The role of nitric oxide (NO) in the initiation, promotion and progression of cancer has been the subject of speculation and conflicting reports in the literature. The high incidence of oral cancer and precancer has been linked to tobacco chewing and smoking habits; NO is considered an indicator of tobacco-related diseases. We compared salivary NO levels in oral precancer and normal patients. Unstimulated whole saliva was collected from 15 patients with oral precancer (group 1) and 15 healthy age and sex matched subjects (group 2). Salivary nitrite levels were estimated using a colorimetric method and a spectrophotometer. The salivary nitrite concentration of group 2 (median = 4.21 μg/ml) was significantly less than for group 1 (median = 12.91 μg/ml). We have added evidence concerning involvement of NO in the pathogenesis of oral cancer, but whether it is a potentially carcinogenic agent at the concentration at which it is present in oral precancer patients requires further evaluation.

Expression of inducible nitric oxide synthase in keratocystic odontogenic tumour and variants of ameloblastoma - a comparative study

INTRODUCTION

The odontogenic keratocyst (OKC) is a histopathologiocally and behaviourally unique and specific entity. It is the most aggressive and recurrent of all the cysts and shows characteristics resembling both cyst and a tumour. The unique nature of OKC and the recent shift of OKC as a tumour made us evaluate yet another factor, Inducible nitric oxide synthase an (iNos) enzyme which has been implicated in the tumourigenesis of various neoplasms. Aims and Objects: The objective of the study was to analyse and compare the immunohistochemical expression of iNOS in odontogenic keratocysts (OKC's) in variants of ameloblastoma affecting the oral cavity, to determine the neoplastic potential of OKC and to reinforce the classification of OKC as keratocystic odontogenic tumour.

MATERIALS AND METHODS

Thirty two specimens, eight specimens each in OKC, follicular ameloblastoma, plexiform ameloblastoma and unicystic ameloblastoma, taken from the Oral Pathology Department were randomly selected for this study and were evaluated for epithelial expression of iNOS by immunohistochemistry Results: Epithelial immunoreactivity to iNOS was strongly positive in 93.5% of follicular ameloblastomas, 68.7% of plexiform ameloblastomas, 66.9% of odontogenic keratocysts and 66.2% of unicystic ameloblastomas.

CONCLUSION

iNOS may be an important marker involved in the biological behaviour of OKC. Furthermore the presence of increased expression of iNOS in Follicular ameloblastomas followed by Plexiform ameloblastomas, OKCs and Unicystic ameloblastomas is yet another evidence to support that OKC could be considered as a neoplasm.

Expression of inducible nitric oxide synthase in the epithelial linings of odontogenic keratocyst, dentigerous cyst and radicular cyst: a pathological insight

BACKGROUND

The present study is aimed at analyzing the expression of inducible nitric oxide synthase (iNOS) in the epithelial lining of odontogenic keratocyst (OKC), dentigerous cyst (DC), radicular cyst (RC) in order to understand the possible role of iNOS with special reference to its neoplastic nature and local aggressive of cysts.

AIM

The primary aim of the following study is to analyze the immunohistochemical expression of iNOS and secondary aim is to compare the iNOS expression, pattern and intensity of staining among the epithelial linings of OKC, DC and RC.

MATERIALS AND METHODS

iNOS in the epithelial lining cells were analyzing in 10 OKC's, 10 DC's and 10 RC's using immunohistochemistry. The percentage of positive cells was assessed and presented as mean ± standard deviation. The correlation with respect to the intensity and percentage of staining within the epithelial linings of OKCs, DCs and RCs was carried out using (analysis of variance and Student's t-test) Chi-square test.

RESULTS

Staining intensity of iNOS portion was seen in the entire thickness of the epithelial linings of OKC, whereas in DC's only one case had entire thickness of the epithelial lining staining and in RC's none of the cases showed entire thickness of staining. On comparing the staining intensity of iNOS between OKC, DC and RC groups, using Chi-square test, there was a statistically significant difference between these groups (P < 0.01). On analyzing the immuno-reactivity of iNOS in OKC, DC and RC there was a positive variable expression iNOS between the cysts.

CONCLUSION

iNOS was over expressed in OKCs when compared with DC and RC suggesting that iNOS may contribute to the aggressive behavior of OKC. This is yet another evidence to support that OKC is the neoplasm.

Nitric oxide synthase 2 (NOS2) expression in histologically normal margins of oral squamous cell carcinoma

The activity of Nitric Oxide Synthase 2 (NOS2) was found in oral squamous cell carcinomas (OSCC) but not in normal mucosa. Molecular changes associated to early carcinogenesis have been found in mucosa near carcinomas, which is considered a model to study field cancerization. The aim of the present study is to analyze NOS2 expression at the histologically normal margins of OSCC.

STUDY DESIGN

Eleven biopsy specimens of OSCC containing histologically normal margins (HNM) were analyzed. Ten biopsies of normal oral mucosa were used as controls. The activity of NOS2 was determined by immunohistochemistry. Salivary nitrate and nitrite as well as tobacco and alcohol consumption were also analyzed. The Chi-squared test was applied.

RESULTS

Six out of the eleven HNM from carcinoma samples showed positive NOS2 activity whereas all the control group samples yielded negative (p=0.005). No statistically significant association between enzyme expression and tobacco and/or alcohol consumption and salivary nitrate and nitrite was found.

CONCLUSION

NOS2 expression would be an additional evidence of alterations that may occur in a state of field cancerization before the appearance of potentially malignant morphological changes.

iNOS-selective inhibitors for cancer prevention: promise and progress

Nitric oxide (NO) is involved in various physiological functions and its role in tumorigenesis has been well studied. A large majority of human and experimental tumors appear to progress owing to NO resulting from iNOS, further stimulated by proinflammatory cytokines. Conversely, in some cases, NO is associated with induction of apoptosis and tumor regression. This dichotomy of NO is largely explained by the complexity of signaling pathways in tumor cells, which respond to NO very differently depending on its concentration. In addition, NO alters many signaling pathways through chemical modifications, such as the addition of S-nitrosothiols and nitrosotyrosine to target proteins altering various biological pathways. Hence, iNOS inhibitors are designed and developed to inhibit various organ site cancers including the colon. Here, we review iNOS expression, generation of NO, involvement of NO in altering signaling pathways, and iNOS select inhibitors and their possible use for the prevention and treatment of various cancers.

Nitric oxide and oral cancer: a review

Nitric oxide (NO), a short-lived, endogenously produced gas, plays key role in various physiological as well as pathological processes. NO-inducing cell signaling events within the cell producing it and the diffusibility of it in other cells have led to the discovery of various physiological functions of NO including vasodilation, respiration, cell migration, immune response and apoptosis. On the other hand, excessive and unregulated NO synthesis has been implicated in many pathophysiological conditions including cancer. Research on NO, during the past few years is one of the growing areas in cancer biology. The high incidence of oral cancer and precancer has been linked with habits of tobacco chewing and smoking and NO has been said as the "messenger of death" in tobacco related diseases. NO seems to play a part in various stages of carcinogenesis from initiation to progression. However, there is considerable controversy and confusion in understanding its role in cancer biology. It is said to have both, tumoricidal as well as tumor promoting effects and these depend on its timing, location and concentration. Further, NO has also been shown to have antitumor, chemopreventive and therapeutic abilities. Here is an overview in which efforts are made to understand the role of this molecule in oral carcinogenesis.

Is Nitric Oxide (NO) the Last Word in Radiosensitization? A Review

As a short-lived radical that diffuses across membranes, rather than interacting with membrane-bound receptors, nitric oxide (NO) represents a significant departure from synthetically derived radiosensitizers. An endogenous compound, NO may equal or surpass its molecular cousin, oxygen, as a hypoxic radiosensitizer, through pleiotropic phenotypic effects on tumor perfusion, cell signaling, mitochondrial respiration, the fixation of radiation-induced damage, and the radioprotection of normal tissue. However, unlike oxygen, in the context of radiosensitization, the clinical role and utility of NO are poorly understood, with often contradictory and controversial reported effects: whether NO functions as a radiosensitizer may ultimately be contextual to the tumor microenvironment. This may make NO manipulation an ideal candidate for a personalized radiosensitization approach tailored to specific patient and tumor types/microenvironmental characteristics. Effective delivery of NO both systemically and directly to the tumor may be critical to the success of this approach. Compounds that release NO or NO precursors have the potential to drive innovation and result in a new fertile branch of the radiosensitizer tree.

Chemoprevention of Colon Cancer by iNOS-Selective Inhibitors

Nitric oxide (NO) is a short-lived pleiotropic regulator and is required for numerous pathophysiological functions, including macrophage-mediated immunity and cancer. It is a highly reactive free radical produced from l-arginine by different isoforms of NO synthases (NOSs). Sustained induction of inducible NOS (iNOS) during chronic inflammatory conditions leads to the formation of reactive intermediates of NO, which are mutagenic and cause DNA damage or impairment of DNA repair, alter cell signaling, and promote proinflammatory and angiogenic properties of the cell, thus contributing to carcinogenesis. Besides its well-established role in inflammation, increased expression of iNOS has been observed in colorectal tumors and other cancers. NO-related signaling pathways involved in colon tumorigenesis seem to progress through stimulation of proinflammatory cytokines and via posttranslational protein modifications of important antiapoptotic molecules in the tumors. NO can stimulate and enhance tumor cell proliferation by promoting invasive, angiogenic, and migratory activities. In contrast, studies also suggest that high levels of NO may be protective against tumor growth by inducing tumor cell death. However, a number of in vitro studies and particularly experimental animal data support the notion that NO and its reactive metabolite peroxynitrite stimulate cyclooxygenase-2 activity, leading to generation of prostaglandins that enhance tumor growth. These prostaglandins further augment tumor promotion and invasive properties of tumor cells. Hence, selective inhibitors of iNOS and combination strategies to inhibit both iNOS and cyclooxygenase-2 may have a preventive role in colon cancer.

Genetics/epigenetics of oral premalignancy: current status and future research

Squamous cell carcinoma (SCC) of the oral and oropharyngeal region is the sixth most common malignancy in the world today. Despite numerous advances in treatment, long-term survival from this disease remains poor. Early detection can decrease both morbidity and mortality associated with this neoplasm. However, screening for potentially malignant disease is typically confounded by difficulty in discriminating between reactive/inflammatory lesions vs those lesions that are premalignant in nature. Furthermore, the histologic diagnosis of dysplasia can be subjective and is thus prone to a considerable range of interpretation. Similarly, no definitive, validated criteria exist for predicting which dysplastic lesions are most likely to progress to cancer over time. Given this state of science, the presence of dysplasia can only be used to indicate that an oral lesion may have an increased risk of malignant transformation. Molecular biomarkers capable of identifying the subset of lesions likely to progress to cancer are required to eliminate this clinical diagnostic dilemma. The purpose of this review is to assess the current state of knowledge regarding genetic/epigenetic alterations observed in oral mucosal premalignancy. In addition, recommendations for future research studies directed at defining the predictive capacity of specific biomarkers in this modeling are presented.

Inducible nitric oxide synthase expression and its prognostic significance in colorectal cancer

Nitric oxide synthases (NOS) are expressed in colorectal cancer. The aim of this study was to examine the inducible NOS (iNOS) expression in colorectal cancer and to investigate its prognostic relevance. Tissue sections of primary tumors from 132 patients undergoing curative resection for colorectal cancer were immunohistochemically examined for iNOS expression. The expression pattern of iNOS was correlated with various clinicopathological characteristics and survival. iNOS immunoreactivity was observed in the cytoplasm of tumor epithelial cells in 60 patients (45.5%) and positively correlated with lymph node involvement (p = 0.019). No significant correlation was found between iNOS expression and various clinicopathological characteristics, including age, gender, tumor location, tumor size, tumor grade, T stage, and Union International Contra la Cancrum (UICC) stage. Survival analysis showed a significant correlation between iNOS-positive tumors and poor disease-specific survival (p < 0.0001), with independent prognostic significance in multivariate analysis (HR = 4.42; p < 0.0001). Patients with stage II disease and iNOS-positive tumors had significantly worse disease-specific survival than those with iNOS-negative tumors (p < 0.0001). In addition, patients with stage III disease and iNOS-positive tumors had significantly worse disease-specific survival than those with iNOS-negative tumors (p = 0.001). The ability of iNOS to predict outcome in colorectal cancer patients may be independent of other known prognostic factors, providing a new molecular marker with significant potential for clinical utility.

iNOS expression in oral and gastrointestinal tract mucosa

It is known that the overproduction of nitric oxide (NO) by nitric oxide synthase (NOS) occurs during the progression of various inflammatory diseases in intestinal tract. NOS inhibitors or inducible nitric oxide synthase (iNOS) gene expression inhibitors should be considered as potential anti-inflammatory agents, as NO synthesized by iNOS is related to various pathophysiological processes including inflammation. In order to understand the relationship between iNOS and pathological reactions such as the inflammatory process and malign transformation clearly, the existence and amount of constitutive expression should be determined. It is crucial to comprehend the harmful and protective amounts of iNOS expressions in order to clarify the relationship between iNOS and pathological processes. Evidently, only after this inspection is it possible to utilize iNOS as a marker and treatment instrument during the diagnosis and treatment of malign transformation and the inflammatory process.

8-Nitroguanine formation in oral leukoplakia, a premalignant lesion

Oral leukoplakia is a premalignant lesion associated with development of oral cancer. To clarify the mechanism of development of oral carcinogenesis from leukoplakia, we examined DNA damage in oral epithelium of biopsy specimens of patients with leukoplakia by immunohistochemical methods. Histological changes, such as epithelial dysplasia and infiltration of inflammatory cells were observed in oral tissues of leukoplakia patients. A double immunofluorescence labeling study demonstrated that the accumulation of mutagenic 8-nitroguanine, an indicator of nitrative DNA damage, and 8-oxo-7,8-dihydro-2'-deoxyguanosine, an indicator of oxidative DNA damage, was apparently observed in the oral epithelium of patients with leukoplakia, whereas little or no immunoreactivity was observed in normal oral mucosa. Expression of inducible nitric oxide synthase (iNOS) was also observed in oral epithelium of leukoplakia patients. Immunoreactivity of 3-nitrotyrosine, an indicator of nitrative stress, was observed in oral epithelial cells and colocalized with 8-nitroguanine. Moreover, proliferating cell nuclear antigen and p53 were expressed in 8-nitroguanine-positive epithelial cells in the basal layer. These results suggest that iNOS-mediated nitrative stress contributes to development of oral carcinogenesis from leukoplakia through DNA damage as well as oxidative stress.

Inhibitory effect of inducible nitric oxide synthase inhibitors on DMBA-induced hamster buccal-pouch squamous-cell carcinogenesis

We investigated the effects of two NOS inhibitors (AG and l-NAME) on DMBA-induced hamster buccal-pouch carcinogenesis. Six hundred Syrian golden hamsters were split into two divisions (I and II); divisions split into three groups (experimental groups A and B, control group C); and each group into subgroups of 20 (A1-A6, B1-B6 and C1-C3). The pouches of animals in groups A1-A3 were painted first with AG of differing concentrations (10, 20, and 30 micromol/ml) and then 30 min later with DMBA (0.5%), thrice weekly for 9 weeks. Subgroups A4-A6 only received AG treatment. Groups B1 to B6 were similarly treated with l-NAME. Animals in division II were treated in the same manner for 13 weeks. Post-mortem analysis revealed that both inhibitors can suppress the development of epithelial dysplasias and squamous-cell carcinomas. An associated increase in the numbers of epithelial hyperplasias was paralleled by a decrease in iNOS protein expression. This animal model can be employed to evaluate the potential use of iNOS inhibitors as novel therapeutic tools for oral squamous-cell carcinogenesis.

Expression of endothelial nitric oxide synthase and vascular endothelial growth factor in oral squamous cell carcinoma: its correlation with angiogenesis and disease progression

BACKGROUND

Angiogenesis is a crucial step in the successful growth, invasion, and metastasis of a tumor. It has been popularly accepted that vascular endothelial growth factor (VEGF) is the most potent angiogenic factor in tumor angiogenesis. As another possible star molecule responsible for tumor angiogenesis, the role of nitric oxide (NO) in tumor biology has gained much attention in recent years. The aim of this study was to investigate whether the expression of endothelial nitric oxide synthase (eNOS) and VEGF in oral squamous cell carcinoma (OSCC) is associated with angiogenesis. The present study also made a preliminary exploration of the possible cross-talking existing between eNOS and VEGF during tumor angiogenesis.

METHODS

In this study, expression of eNOS and VEGF were studied immunohistochemically in tissue sections from 40 patients with OSCC and 20 normal controls. To exclude eNOS antibody cross-reactivity with inducible or neuronal nitric oxide (iNOS or nNOS), eNOS expression was confirmed by using an eNOS mRNA in situ hybridization kit. The intratumoral microvessels were highlighted by immunostaining with anti-factor VIII-related antigen monoclonal antibody and counted as well-established methods. Then, chi-square test or Student's t-test was performed to study the correlations between the expression of eNOS and VEGF, microvessel density (MVD), and various clinicopathologic factors.

RESULTS

Both eNOS and VEGF expression significantly increased in OSCC tissues, with a positive rate of 47.5% and 50%, respectively. The average MVD in OSCC tissues was 23.45 per high-power field (HPF), showing an obvious association with lymph node metastasis and clinical stages of patients with OSCC. Either eNOS or VEGF positivity was correlated with vessel involvement and OSCC progression. The mean MVD was significantly higher in eNOS- or VEGF-positive tumors than in eNOS- or VEGF-negative tumors. An obvious, correlation was also seen between eNOS and VEGF expression in OSCC tissues in this study.

CONCLUSIONS

Overexpression of eNOS and VEGF might make an important contribution to the tumor angiogenesis in OSCC. NO generation by eNOS might be implicated in the VEGF-associated angiogenic process. Further investigation of the possible cross-talking between eNOS and VEGF with respect to tumor angiogenesis is necessary.

Correlation between inducible nitric oxide synthase and p53 expression for DMBA-induced hamster buccal-pouch carcinomas

Three isoforms of nitric oxide synthase (NOS) have been identified previously--endothelial NOS, neuronal NOS, and inducible NOS (iNOS). It has been reported previously that there may be a negative feedback loop existing between nitric oxide (NO) production and wild-type p53 tumor-suppressor gene, but the relationship has not previously been studied for oral experimental carcinogenesis. The purpose of the present study is to assess whether iNOS expression correlates with p53 expression at both protein and mRNA levels for 7,12-dimethylbenz[a]anthracene (DMBA)-induced hamster buccal-pouch carcinomas.

MATERIALS AND METHODS

Thirty-five out-bred, young (6 week old), male, Syrian golden hamsters (Mesocricatus auratus) were randomly divided into one experimental group (15 animals), and two control groups (10 animals each). Bilaterally, the pouches of a group of 15 animals from the experimental group were painted with a 0.5% DMBA solution three times a week for 12 weeks whilst each animal from one of the control groups was similarly treated with only mineral oil. Another control group of 10 animals remained untreated throughout the experimental procedure. Specimens obtained from the hamster buccal-pouch mucosa were evaluated using immunohistochemical assessment of iNOS and p53 protein and in situ reverse transcription-polymerase chain reaction (IS RT-PCR), as well as reverse transcription-polymerase chain reaction (RT-PCR) for iNOS and p53 mRNA.

RESULTS

Two of the 15 animals of the DMBA-treated group died during the experiment. Squamous-cell carcinomas with a 100% tumor incidence were apparent for all of the 15-week DMBA pouch-treated animals. Animals from the mineral oil-treated and untreated pouch groups revealed no obvious changes. Inducible NOS mRNA was identified as a band corresponding to a 499-bp PCR product and was observed for all 13 of the hamster buccal-pouch tissue specimens treated with DMBA for 15 weeks. The p53 mRNA was found as a band corresponding to a 370-bp polymerase chain reaction (PCR) product and was noted for nine (9/13, 69%) of the 15-week DMBA-treated pouches. No such bands (iNOS and p53) were noted for the untreated animals, the mineral oil-treated tissues and the negative-control samples. Using IS RT-PCR, the proportional (percentage) expression of iNOS (13/13, 100%) and p53 (8/13, 62%) mRNA observed for the hamster buccal-pouch tissue specimens treated with DMBA for 15 weeks was noted to be consistent with the findings using RT-PCR. Furthermore, the proportional expression of iNOS (13/13, 100%) and p53 (8/13, 62%) proteins for the 15-week DMBA-treated hamster buccal-pouch tissue specimens was noted to be consistent with the findings using RT-PCR and IS RT-PCR. A significant association between iNOS and p53 expression (at both protein and mRNA levels) was noted (Fisher's exact probability test, P < 0.05). Neither iNOS nor p53 activity (at both protein and mRNA levels) was found for any of the untreated and mineral oil-treated pouches.

CONCLUSIONS

Enhanced expression of iNOS and p53 at both protein and mRNA levels in DMBA-induced hamster buccal-pouch carcinomas compared with the untreated and mineral oil-treated counterparts, has been demonstrated in the current study. Furthermore, we report what is, to the best of our knowledge, the first identification of a significant association between iNOS and p53 expression (at both protein and mRNA levels) in this experimental model system for oral carcinogenesis, although their precise interactions remain to be clarified.

The role of nitric oxide in oral diseases

Although previously regarded as a toxic pollutant gas, nitric oxide (NO) is a short-lived molecule that plays a key role in many physiological and pathological processes. It is produced in vivo from the amino acid L-arginine by a complex family of enzymes termed nitric oxide synthase (NOS). Since its discovery as a biological messenger in 1987, NO has been implicated in many disease processes, ranging from septic shock to cancer. It is a highly reactive free radical and causes concentration-dependent conformational changes in proteins, enzymes and DNA, predominantly by its reaction with transition metals and thiol residues. Although high concentrations of NO are cytotoxic, the levels produced in many human cancers possibly facilitate tumour growth and dissemination. The interest in this molecule by scientists and clinicians involved with the oral cavity and head and neck regions is fairly recent, and only a tiny minority of 50,000 papers currently cited on NO relate to diseases in this anatomical area. This review gives an overview of NO, outlining its basic chemistry, formation by NOS and its possible roles in the oral diseases studied to date. The implications for possible therapeutic manipulation of NO are also discussed.

Increased expression of inducible nitric oxide synthase for human oral submucous fibrosis, verrucous hyperplasia, and verrucous carcinoma

Three isoforms of nitric oxide synthase (NOS), endothelial, neuronal and inducible NOS (iNOS), have been identified in humans. Enhanced expression of iNOS protein has been previously reported for human oral epithelial dysplasias, a human oral premalignant epithelial lesion; however, this expression has not been demonstrated for other premalignant epithelial lesions, namely, oral submucous fibrosis (SF) and verrucous hyperplasia (VH). On the other hand, iNOS protein expression has not been reported in human oral verrucous carcinoma (VCa). The aim of this current study was to determine whether iNOS protein also occurs for oral SF, VH and VCa lesions. We found that membranous stainings were observed chiefly in oral SF lesions (17/20, 85%), whereas cytoplasmic stainings were mainly found in the VH variants (16/20, 80%). By contrast, cytoplasmic and/or nuclear stainings were observed in the specimens of verrucous carcinoma (17/20, 85%). Since no iNOS activity could be detected for any of our specimens of normal buccal mucosa in the present immunohistochemical study, this suggests that an NOS-dependent mechanism may be involved in the malignant transformation of these two premalignant oral epithelial lesions.

Oral lichen planus has a high rate of TP53 mutations. A study of oral mucosa in icelanD

Oral squamous cell carcinoma (OSCC) is a world-wide health problem. In addition to external exposure (smoking and alcohol), certain oral lesions may increase the risk of oral cancer (e.g. leukoplakia, erythroplakia, and oral lichen planus). TP53 has been implicated in OSCC, but there are limited studies of mutations in premalignant oral lesions. In this study, 55 samples from OSCC, 47 from hyperkeratotic (HK) oral mucosa, clinically diagnosed as white patches, 48 samples from oral lichen planus (OLP), and 12 biopsies from normal oral mucosa were studied immunohistochemically for expression of TP53 protein. From all the carcinoma samples and selected non-malignant samples showing moderate or strong TP53 protein expression, malignant cells or TP53-positive nuclei were microdissected and screened for mutations in exons 5-8 by constant denaturation gel electrophoresis. Moderate to strong TP53 protein staining was seen in 56% of OSCC, 32% of OLP but only in 13% of HK. All OLP samples showed a characteristic pattern of positive nuclei confined to the basal layer, whereas TP53 staining was seen in suprabasal nuclei in HK. Mutation rate was 11 out of 52 for OSCC, three out of 20 tested for HK and, remarkably, nine out 27 tested for OLP. There was no correlation between TP53 protein staining and TP53 mutations. No associations were found with anatomical sites or disease progression. The unexpectedly high mutation rate of OLP might explain the premalignant potential of this lesion.

The mRNA expression of inducible nitric oxide synthase in DMBA-induced hamster buccal-pouch carcinomas: an in situ RT-PCR study

Three isoforms of nitric oxide synthase (NOS) have been identified: endothelial NOS, neuronal NOS, and inducible NOS (iNOS). The enhanced expression of iNOS at the protein level using immunohistochemical technique has been reported previously in chemically induced oral carcinomas in hamster buccal-pouch mucosa. However, the corresponding expression of iNOS at the mRNA level has not yet been demonstrated using in situ reverse transcription-polymerase chain reaction (IS RT-PCR). The purpose of the present study is to assess the iNOS mRNA expression level in 7,12-dimethylbenz[a]anthracene (DMBA)-induced hamster buccal-pouch carcinomas using IS RT-PCR. Thirty outbred, young (6-weeks old), male, Syrian golden hamsters (Mesocricatus auratus) were randomly divided into one experimental group (10 animals), and two control groups (10 animals each). The pouches of a group of 10 animals of the experimental group were painted bilaterally with a 0.5% DMBA solution three times a week for 15 weeks. Each animal of one of the control groups was similarly treated with only mineral oil. Another control group of 10 animals remained untreated throughout the experiment. Invasive squamous-cell carcinomas with a 100% tumour incidence developed in all of the DMBA-treated buccal pouches. The mineral oil-treated and untreated pouches revealed no obvious changes. Inducible NOS mRNA was demonstrated amongst all the 15-week DMBA-treated hamster buccal-pouch mucosa animals, but not in the untreated animals and not in the animals for which the buccal-pouch was treated with mineral oil. Further study is necessary to evaluate the mechanism(s) which contribute to the increased iNOS mRNA expression for experimentally induced oral carcinogenesis.

Expression of inducible nitric oxide synthase in human oral premalignant epithelial lesions

Increased expression of inducible nitric oxide synthase (iNOS) has been found at the protein level in human oral epithelial dysplasias, but, a corresponding expression at the mRNA level has not been demonstrated. The purpose here was to assess the expression of iNOS mRNA and its correlation with the expression of the enzyme protein in human buccal premalignant epithelial lesions. Activities for iNOS protein (57/80, 64%) and mRNA (53/80, 53%) were detected in the specimens examined. Cytoplasmic and/or nuclear staining for iNOS protein was detected immunohistochemically in a number of mild oral epithelial dysplasias (16/20, 80%), moderate to severe oral epithelial dysplasias (14/20, 70%), submucous fibrosis (14/20, 70%) and verrucous hyperplasia (13/20, 65%). Upon in situ reverse transcription-polymerase chain reaction (RT-PCR), the cellular location of iNOS mRNA was compatible with the immunohistochemical findings. Furthermore, iNOS mRNA was found in 15 specimens of mild oral epithelial dysplasia (15/20, 75%), 13 specimens of moderate to severe oral epithelial dysplasia (13/20, 65%), 13 specimens of submucous fibrosis (13/20, 65%) and 12 specimens of verrucous hyperplasia (12/20, 60%). No iNOS protein or mRNA was found in samples of normal buccal mucosa, or in negative controls. Further studies on the characteristics of iNOS-positive cells and more long-term clinical follow-up data are needed.

Expression of type 2 nitric oxide synthase and p21 in oral squamous cell carcinoma

Nitric oxide (NO) has a complex role in tumour biology. Most cancer research has focused on the enzyme nitric oxide synthase-2 (NOS2), an inducible isoform responsible for prolonged NO production. In normal cells exposed to high NO concentrations, the tumour-suppressor gene, p53, promotes apoptosis via the p21 pathway, in an attempt to safeguard against potential NO-mediated DNA damage. In cancer cells with mutant p53, this pathway is unlikely to occur directly, although, p53-independent p21 expression and subsequent apoptosis can occur at higher NO concentrations. In this study, the possible direct association between NOS2 and p21 was assessed in oral squamous cell carcinoma. Immunohistochemistry was performed for NOS2 and p21 on 56 cases, and NOS2 activity was determined with citrulline assays in selected cases. A significant relationship was demonstrated between the immunohistochemical expression of NOS2 and its activity (P<0.001), but not between NOS2 and p21 expression (P=0.76). It is unlikely that the NO concentrations found in oral cancer (up to 10.3 pmol NO min(-1) mg protein(-1)) are sufficient to cause direct (p53-independent) p21 accumulation and subsequent apoptosis. As with many other tumours, since NO production has a detrimental role, its pharmacological inhibition in oral cancer represents an exciting area for possible future therapeutic manipulation.

The mRNA expression of inducible nitric oxide synthase in DMBA-induced hamster buccal-pouch carcinomas using reverse transcription-polymerase chain reaction

BACKGROUND

Three isoforms of NO synthase (NOS) have been identified: endothelial NOS, neuronal NOS, and inducible NOS (iNOS). The enhanced expression of iNOS, at the protein level, has been reported previously in certain chemically induced oral carcinomas in hamster buccal-pouch mucosa, however, the corresponding expression of iNOS, at the mRNA level, has not yet been demonstrated. The purpose of the present study is to assess the iNOS mRNA expression level in 7,12-dimethylbenz[a]anthracene (DMBA)-induced hamster buccal-pouch carcinomas using a reverse transcription-polymerase chain reaction (RT-PCR).

METHODS

Thirty-three outbred, young (six-weeks old), male, Syrian golden hamsters (Mesocricetus auratus) were randomly divided into one experimental group (13 animals) and two control groups (10 animals each). The pouches of a group of 13 animals of the experimental group were bilaterally painted with a 0.5% DMBA solution three times a week for 12 weeks. Each animal of one control group was similarly treated with mineral oil only, while the other control group of 10 animals remained untreated throughout the experiment.

RESULTS

Areas of dysplasia and squamous-cell carcinomas, with a 100% tumor incidence, developed for all of the DMBA-treated buccal pouches. The mineral oil-treated and untreated pouches had no obvious changes. A band of 499-bp, corresponding to iNOS mRNA, was present in all the DMBA-treated hamster buccal-pouch mucosa animals, but not in the untreated animals or the animals treated with mineral oil. Upon direct sequencing, this 499-bp band was confirmed to be part of the iNOS gene.

CONCLUSIONS

This study demonstrated that increased iNOS mRNA expression could contribute to the mechanism for experimentally induced oral carcinogenesis.